Photonic flash sintering of silver nanoparticle inks: a fast and convenient method for the preparation of highly conduct
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Photonic flash sintering of silver nanoparticle inks: a fast and convenient method for the preparation of highly conductive structures on foil Robert Abbel, Tim van Lammeren, Rob Hendriks, Jeroen Ploegmakers, Eric J. Rubingh, and Erwin R. Meinders, Holst Centre – TNO, High Tech Campus 31, 5656 AE Eindhoven, The Netherlands Wilhelm A. Groen, Holst Centre – TNO, High Tech Campus 31, 5656 AE Eindhoven, The Netherlands; Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands Address all correspondence to Wilhelm A. Groen at [email protected] (Received 15 August 2012; accepted 13 November 2012)
Abstract Silver nanoparticle inks printed on temperature-sensitive substrates can be converted into structures with high electrical conductivities within fractions of a second by photonic flash sintering. The key principle is the selective heating of the ink by the absorption of strongly focused pulsed light for which the substrate is transparent. The influence of process parameters like intensity and flashing frequency on the sintering speed is investigated. Furthermore, a setup is demonstrated for monitoring the temperature development in an ink during flash sintering, revealing that the substrate’s glass transition point is exceeded only for very short time intervals, which prevents deformation.
Introduction Conductive inks based on highly concentrated metal nanoparticle dispersions are important materials in the fabrication of printed electronic devices such as organic light-emitting diodes (OLEDs) and organic photovoltaic (OPV) cells.[1,2] Their primary purpose is the production of highly conductive, patterned metal structures that serve as shunting lines or current collecting grids in order to reduce resistive losses in the transparent electrodes.[3–5] When applied to flexible plastic substrates, these materials allow fast high-volume production techniques to be applied, such as roll-to-roll manufacturing.[6,7] Since the conductivities of the as-deposited nanoparticle inks are generally poor, a post-deposition treatment is needed to enhance them, which is generally achieved by applying heat, usually in a hot air oven,[6,7] but IR irradiation has been used as well.[8] Since, however, the commonly used inexpensive polymer foils (e.g., PET (poly(ethylene terephthalate)) or PEN (poly (ethylene naphthalate)) lose their dimensional stability well below 150 °C (glass temperatures 100–105 °C (PET) and 125–130 °C (PEN); cf. Supplementary Information), thermal sintering is limited to rather low temperatures. As a consequence, relatively long sintering times are needed to achieve a reasonable functional performance.[6–8] Alternatively, (near) room temperature sintering methods have been developed that achieve the formation of conductive structures by chemical rather than thermal processes. The most important examples are plasma sintering,[9] which, however, is generally rather slow, and chemical sintering,[10–13] which often involves wet chemical steps or exposure to vap
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